In recent years, in order to reduce environmental load, a power generation system utilizing natural energy such as solar power generation, that does not emit carbon dioxide is spreading into homes. For example, Patent Document 1 shown below discloses a configuration of a power feed system in which solar power generation and a storage battery are combined to supply power to a system in coordination with each other, and a control technique for the power feed system.
Specifically, the power feed system includes a first DC/DC converter for converting first DC voltage from the solar power generation to second DC voltage, a second DC/DC converter for converting third DC voltage from the storage battery to fourth DC voltage, a supply section for connecting outputs of the first and second DC/DC converters to a load, and a DC/AC inverter for synchronizing DC voltage from the supply section with an AC voltage waveform supplied from a system, to output AC power. Then, the following method is described as an example. In peak-cutting for solving power shortage, in the case where the solar power generation is prioritized to supply power to the AC load, a target DC voltage value for generation of the second DC voltage by the first DC/DC converter is set to be higher than a target DC voltage value for generation of the fourth DC voltage by the second DC/DC converter, whereby generated power by the solar power generation is preferentially supplied to the AC load.
Upon power outage, power generation using natural energy represented by solar power generation can only output the maximum power of 1500 W from an autonomous operation outlet provided in advance in a power conversion device. Meanwhile, after Great East Japan Earthquake, in order to cope with power shortage or the like, various companies are developing and producing a system having a storage battery, a system using an electric automobile as a storage battery, a system combining solar power generation and a storage battery, and the like. In the above systems, a lithium-ion battery is often used as a storage battery.